/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) 
    {
        if(headA == NULL || headB == NULL)
            return NULL;

        ListNode* pA = headA;
        ListNode* pB = headB;

        while(pA != pB)
        {
            pA = (pA == NULL ? headB : pA -> next);
            pB = (pB == NULL ? headA : pB -> next); 
        }

        return pA; 
    }
};